Combined convex and concave auger



'UNITED sTATEs PATENT oEETcE.

NATHL. C. SANFORD, OF MERIDEN, CONNECTICUT.

C01VI]2-I]\TE'|D CONVEX AND CONCAVE AUGER.

Specification of Letters Patent No. 6,221, dated March 27, 1849.

To'aZZ whom t may concern Be it known that I, NATHANIEL C. SAN- FORD, ofthe town of Meriden, in New Haven county and State of Connecticut, haveinvented a new and useful Improvement in Form and Construction ofConcave Screw- Angers.

My improvement consists as follows. Instead of having the plate fromwhich the auger is to be twisted of concaved shape throughout as isusual in forming concave angers, I form the lower extremity of the plateof convex shape, or of even thickness, though the former is preferred.In an auger of five eighths diameter it will be sufficient to have aboutan inch of the lower extremity of convex shape or of even thickness asaforesaid, varying in proportion as the diameter of the auger isincreased or diminished.

The advantage of this mode of constructhe plate a short twist. at thelower eX- tremity and finish the cutting lips or edges in the best andmost approved method for easy boring, than when the plate is formed inthe usual way of concave shape throughw out.

That I claim as my invention and desire to secure by Letters Patent is-Forming the lower part of the plate from which an auger' is to beformed, of a convex shape or of even thickness, when this is combinedwith the upper part of the plate formed of a concave shape. The wholeplate being formed for the purpose of making therefrom a double lippedconvex and concave auger.

In witness whereof I have hereto set my hand and seal this twenty thirdday of October A. D. 1848.

NATHANIEL' C. SANFORD.

In presence of- Cris. IV. CURTISS. JN0. S. BEACH.

